1. Field of the Invention
The present invention relates to an electron emission device, and more particularly, to an electron emission device having a grid electrode inside a vacuum vessel to reduce damage by arc discharge.
2. Description of the Related Art
Generally, electron emission devices are classified into those using hot cathodes as the electron emission source, and those using cold cathodes as the electron emission source.
There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a surface conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
The MIM-type and the MIS-type electron emission devices have electron emission regions with a metal/insulator/metal (MIM) structure and a metal/insulator/semiconductor (MIS) structure, respectively. When voltages are applied to the two metals or the metal and the semiconductor respective sides of the insulator, electrons supplied by the metal or semiconductor on the lower side pass through the insulator due to the tunneling effect and arrive on the metal on the upper side. Of the electrons that arrive at the metal on the upper side, those that have energy greater than or equal to the work function of the metal on the upper side are emitted from the upper electrode.
The SCE-type electron emission device includes a thin conductive film formed between first and second electrodes arranged facing each other on a substrate. Micro-crack electron emission regions are positioned on the thin conductive film. When voltages are applied to the first and second electrodes and an electric current is applied to the surface of the conductive film, electrons are emitted from the electron emission regions.
The FEA-type electron emission device uses electron emission regions made from materials having low work functions or high aspect ratios. When exposed to an electric field in a vacuum atmosphere, electrons are easily emitted from these electron emission regions. A front sharp-pointed tip structure based on molybdenum Mo or silicon Si, or a carbonaceous material such as carbon nanotube, graphite and diamond-like carbon, has been developed to be used as the electron emission regions.
Although the above electron emission devices are different in their detailed structures according to the type, they commonly include first and second substrates facing each other. Electron emission regions and driving electrodes are positioned on the first substrate, and an anode electrode and a phosphor layer are positioned on the second substrate, where the first and second substrates form a vacuum vessel. The anode electrode facilitates accelerating the electrons emitted from the first substrate toward the phosphor layer.
The electron emission devices apply the driving voltages to the driving electrodes to emit the electrons from the electron emission regions in each pixel, and the electrons are attracted by the high voltage applied to the anode electrode ((+) voltages ranging from several hundred to several thousand volts) and directed toward the second substrate to collide against the corresponding phosphor layer, thereby performing a predetermined light emission or image display.
The electron emission device performing the above action can secure the stable driving characteristics so long as the vacuumed inner space maintains the electrically stable status with respect to the high anode voltage.
However, in the conventional electron emission devices, since the edge of an active area formed on the first substrate—an area where the electron emission regions and the driving electrodes are formed and the electron emission occurs—faces the anode electrode, the devices can be directly influenced by the anode voltage. The edge of the active area is a region where the continuity of the structures is broken in terms of a plan view of the structures provided on the first substrate.
Due to the above structural characteristics, a stronger electric field can be applied to the edge of the active area than to the center of the active area, or distortion of the electric field can occur. At the worst, there is a problem that causes the abnormal discharge, such as arcing in the edge of the active area, to damage the structures formed on the first substrate.
Further, as the brightness of the screen is proportional to the anode voltage, the anode voltage has been increased accordingly. However, as the anode voltage becomes higher, the possibility of generating abnormal discharge like arcing inside the vacuum vessel is increased.